Or “What is the difference between 4:3 and 16:9?” “Why should I care about aspect ratio?”
Suppose you’re having a meeting for all your top executives and they’ve spent a lot of time putting together presentations with spreadsheets and charts and graphs. The day of the event the first executive loads her slide deck, but the image doesn’t fill the screen. There’s gaps along the edges. You’ve got pretty big screens but the actual presentation seems smaller. What’s the problem? The aspect ratio of the source material and displays don’t match.
The aspect ratio is how wide an image is compared to how tall it is. For example, if a screen has an aspect ratio of 16:9, it could be 16 inches by 9 inches, 16 feet by 9 feet, or 32 feet by 18 feet. Ideally the aspect ratio of your source material and screen will be the same.
Why should you care about aspect ratio? It’s possible you could pay for a wide screen TV but then only show standard 4:3 material leaving gaps on the left and right. That’s space your presenters could have used for charts. Or graphs! You might order a large projection screen and not use the top and bottom due to widescreen content. Not only is there a question of unused space, but some people don’t care for it aesthetically.
As you’re putting together materials ideally you’ll communicate to both your presenters and AV partner what the desired ratio is. That way you’re getting the most bang for your buck, using the screen you paid for and presenting the best version of your content.
In the past the most common format for slideshows like powerpoint in the U.S. was 4:3, but because of the popularity of wide screen TVs increasingly the standard is 16:9. I’m actually simplifying a bit, there’s a huge range of aspect ratios, but for event audio visual in the U.S. these will be the most common. If you’re interested there’s a great wikipedia article with more info.